Carriers Crossing the Pongo River, South Sudan
I sure hope that some little twit, most likely by now long dead, enjoyed that stamp.
Angelo H Capato (the ?publisher) seems to have been a merchant in Khartoum.
The postcard is a Collotype, not an RPP.http://en.wikipedia.org/wiki/Atbarah
The Atbara postmark is straightforward enough.
But the Travelling Post? Shellal? Anybody?